a. Field of the Invention
This invention relates to a method for color-painting on a chromium-plated surface of an object to be painted.
For example, a steering handle tubing, an exhaust pipe, a silencer or muffler pipe, a carrier frame, and so on for a motorcycle is generally plated on their surface with chromium. However, such chromium-plated surface of these tubings is plain in color tone and luster, hence the chromium plating tends to be regarded as featureless and to lose its popularity among the users of the motorcycle.
With a view to avoiding such monotonousness in the outer appearance of these component parts of the motorcycle, and making the motor-operated vehicle more attractive to the users, color-painting on these component parts has been contemplated. For the color-painting, however, there has so far been available delustered silicon resin paint alone which is lack in color sense, and is not suited for those parts such as exhaust pipe and muffler that are subjected to high temperature fatigue during the motorcycle operation.
b. Description of Prior Arts
There has so far been known a method for color-painting on the chromium-plated surface of an object for obtaining an iridescent or shot coating film utilizing luster of the metal material per se, which comprises the following steps: chemical film coating treatment on the metal base.fwdarw.baking the film coated thereon.fwdarw.priming treatment.fwdarw.baking of the primer coating.fwdarw.surface treatment.fwdarw.metal flake (e.g., aluminum powder) application.fwdarw.baking of the metal flake applied.fwdarw.painting of coloring matter.fwdarw.baking of the coloring matter as painted.fwdarw. coating of transparent paint.fwdarw.baking of the transparent paint as coated.
In view of the multiple process steps for coating, not only a great deal of time and coating appliances are necessitated, but also the resulted metal surface is coarse and its transparency is also inferior, because the glossy material used is the metal flake.
In other painting method, there has been known such one that comprises the steps of: chromium plating on the metal base.fwdarw.shot-blasting.fwdarw.air-blowing.fwdarw.primary treatment.fwdarw.baking of the primer coating.fwdarw.surface treatment.fwdarw.baking.fwdarw.coating of coloring matter.fwdarw.baking of the coloring matter.fwdarw.coating of transparent paint.fwdarw.baking of the transparent paint. Even this method, however, does not provide satisfactory surface paint coating, because the chromium-plated surface once formed becomes coarse due to the shot blasting to be effected for improving the adhesive property of the coated film. Further, the chromium-plated surface becomes low in its anti-corrosion property, inferior in its transparency and gloss, and hardly expectable to attain its heat-resistant property to a satisfactory extent.